Take
Control of your USB Development
Chapter
9 of the USB Specification details some seventeen
Standard Device Requests which must be correctly
implemented in any USB device, in order for the
device to be successfully enumerated by the host
controller.
When
developing a USB-based device it is a major undertaking
to implement the basic Chapter 9 Framework correctly
as enumeration will simply fail for any number of
reasons involving incorrect responses to the requests.
There
is no substitute for a USB bus-analyser for revealing
the smallest details of the packet transfers which
takes place on the bus. Software based analysers
can only ever give you a partial picture of what
is going on, usually not reporting at all the packets
with the errors.
The
Packet-Master Analyser connects passively between
a host computer and the USB device, and captures
all USB activity without influencing the link.
Benefits
of Packet-Master Bus Analysers
Choice
of Investment
The
Packet-Master USB12 is a
very cost-effective solution to the development
of USB low speed or full speed devices. Where the
full range of USB speeds is required the Packet-Master
USB480 comes into its own, offering analysis
of any speed and revealing the operation of On-the-Go
technology hosts. An enhanced version of the USB480
with comprehensive triggering functions and a larger
FIFO is now available; the Packet-Master
USB480+.
See
This Month's Special Offer on Packet-Master Analysers
Save
Development Time
A
Packet-Master Bus Analyser will provide you with
exact information showing you at which point a device
under development is failing. It will save you weeks
of wasted development time. In many cases you will
find that the error you are looking for is highlighted
on the Graphic USB display in a distinctive colour.
Simple
Connection
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The
Packet-Master connects passively between a host
computer and the USB device, and captures all
USB activity without influencing the link. So
you can be sure that you are seeing exactly
what really happens. All the important timings
are displayed. |
Understand
USB
| When
it comes to the USB protocol, a picture is worth
a thousand words. The graphical display of Graphic
USB immediately provides deeper understanding
of the data transfers and their related timings.
By examining a working device, you will learn
more in a few minutes than from hours of reading
the specifications. (Specifications are essential
too, but easier to understand when you have
a picture in your mind.) |
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Understand
Host Command Sequences
There
is no specification as to the sequence of commands
which a device may expect from a host. Some command
sequences can be very surprising to the starting-out
developer. The Packet-Master Bus Analyser will allow
you to examine the sequences for any Operating System
/ Host Controller combination of your choice. This
will allow you to reveal any false assumptions you
may be making that a particular enumeration sequence
is standardised.
(As a device developer, just remember that the device
should make no assumptions about enumeration sequences,
but simply respond correctly to any request it receives.)
Examine
Working Devices
A
great benefit available from the Packet-Master Bus
Analyser is that it allows you to examine exactly
what transactions occur in a working device, perhaps
manufactured by a third party. This may reveal your
own bad assumptions about how a protocol works,
or may show you how many devices on the market do
not obey the rules.
Some operating systems have work-arounds for certain
common protocol errors, and you may discover some
of these first-hand.
Specifications often contain ambiguities. For example,
without seeing it for yourself, you might not have
realised that there have been two different ways
of encoding the version number (bcdUSB) for USB
1.1. Operating systems appear to take the pragmatic
approach of accepting either.
Fine-tune
Performance
Much
of the effort in developing a new device will go
into achieving the throughput required. There is
no substitute for seeing the transactions attempted
by the host, together with the device's response
to them. Armed with this valuable information you
will be in the best position to be able to fine-tune
your device's performance.
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